The present invention is directed toward a method and apparatus for homogeneous exposure of video display screen and more specifically to a video game where a television picture tube would have prolonged exposure to a fixed pattern.
When a video game is not in active use (that is, the game is not being played), if it is of the coin-operated type it may still display a fixed pattern in order to attract prospective customers or players. Thus, a playfield may be displayed such as in a paddle and ball game with the outlines of a playing court along with a moving and bouncing ball. This is known as the attract mode.
To implement this attract mode in a ball/paddle game an array of moving squares has been provided such as shown in FIG. 1. The moving pattern was controlled by the same position circuitry as used for the moving ball. Such a pattern did not contribute to the homogeneous exposure of the television tube since the moving pattern was merely ORed with the fixed pattern and thus the fixed pattern remained unchanged. In addition, the moving array of squares did not form a checkerboard pattern but in contrast was inhomogenous and had a duty cycle of perhaps 25%.
Thus the fixed pattern especially in a coin-operated environment had a tendency to expose portions of the television tube phosphors to different amounts of luminance and thus cause uneven wear or aging of the phosphors. This was also true of the chroma or color signal.